Conventionally, many wiper controlling apparatuses used in vehicles have been suggested. In such wiper controlling apparatuses, one of the important factors is a mechanism of sensing raindrops, which is called a rain sensor. As a structural example of a rain sensor using an optical system, there is a known configuration in which light emitted from a photo emission element is reflected by a sensing surface provided on a windshield, and then received by a photo-detector, thereby sensing raindrops. In other words, the photo emission element, the sensing surface and the photo-detector are arranged such that the light reflected by the sensing surface reaches the photo-detector in the state where no object is lying on the sensing surface. Then, when water or the like impacts on the sensing surface, the reflection condition on this surface changes, whereby the amount of light reaching the photo-detector decreases, resulting in a lowered output of the photo-detector. Raindrops have been sensed by recognizing this change.
In the conventional configuration described above, the changes in the light amount often have been identified by the photo-detector by a system of comparison with a predetermined reference value (a threshold method).
Now, these wiper controlling apparatuses are used under various conditions in practice. Therefore, measures have to be taken to prevent their malfunction. Thus, in the rain sensor, a plurality of reference values have been set according to various modes, or the reference value has been updated sequentially according to situations.
In the conventional rain sensor described above, the logic of sensing raindrops has become more complex, thus making it difficult to process the detection judgment at a high speed. Furthermore, all these methods basically judge the condition of the sensing surface and detect raindrops by comparison with the reference value. Therefore, owing to the influence of external light and conditions of the sensing surface such as dirt, it has been difficult to prevent the malfunction completely.
In order to solve such problems, the inventors of the present invention suggested a sensing device and a wiper controlling apparatus using the same, etc. in JP 2001-180447 A, JP 2002-277386 A and JP 2003-306127 A.
JP 2001-180447 A mentioned above disclosed “an object sensor sensing the status of a sensing surface by detecting a light with a photo detector, which light has been emitted by a photo emission element and reflected on the sensing surface, comprising: a means for generating a time lag signal from the output signal of the photo detector; a means for calculating a differential signal between the output signal of the photo detector and the time lag signal; and a means for judging the status of the sensing surface by detecting the generation of the differential signal.”
This technology was characterized by the ability to detect instantly a dynamic process of an impacting raindrop, etc. itself, which was not possible by the conventional technology.
Also, JP 2002-277386 A disclosed “a sensing device in which a light emitted from a light-emitting member is introduced to a transparent plate, reflected by a sensing surface of the transparent plate and then received by a photo-detector, thereby detecting a condition of an object that has impacted on the sensing surface, the sensing device comprising: a sampling part for sampling signals from the photo-detector; a fluctuation sensing part for sensing a fluctuation of the signals from the photo-detector; and a judging part for judging the object based on a changing pattern of the signal fluctuation sensed by the fluctuation sensing part.”
The characteristics of this technology follow. That is, with a dynamic fluctuation of the signal of the photo-detector obtained through the object that has impacted on the sensing surface, it is possible to sense a dynamic jiggling of the lying object indirectly. Furthermore, with the changing pattern of the signal fluctuation, the changing pattern of the lying object's jiggling determined by the lying object's physical properties can be sensed indirectly, thus making it possible to judge the kind and condition of the lying object.
Moreover, in the technology disclosed in JP 2003-306127 A, the two technologies described above are combined so as to control a wiper.
Other than the above, a wiper operating device disclosed in JP 2001-518857 A (WO 98/45148) can perform fog and drizzle identification in addition to rain identification and water droplet identification. In this device, the measurement values of a moisture sensor are associated with incremental values. Each difference value between two successive incremental values is added to the sum of difference values that are signed and previously formed in a similar manner in a memory, and used for controlling a wiping operation.
Additionally, JP 3073632 B discloses “a method comprising the steps of detecting the presence of a falling edge in the sensor signal, the falling edge indicating the presence of moisture on the monitored portion of the windshield; identifying the shape of the falling edge, the wiping system detecting a rain pattern based on the shape and number of falling edges in the sensor signal during a predetermined period of time; and controlling the windshield wiping system based on the identified rain pattern.”
Patent document 1: JP 2001-180447 A
Patent document 2: JP 2002-277386 A
Patent document 3: JP 2003-306127 A
Patent document 4: JP 2001-518857 A
Patent document 5: JP 3073632 B